Determinants of diaphragm ultrasound and its diagnostic performance for predicting respiratory status in myotonic...

Respiratory failure is a leading cause of mortality in patients with myotonic dystrophy type 1 (DM1). Monitoring of respiratory status is recommended in this disease. Ultrasound can be used to assess diaphragm function. We aimed to assess the performance diagnostic of diaphragm ultrasound for predicting respiratory involvement in DM1.

Diaphragm ultrasound and spirometry were performed in DM1 patients in a Parisian neuromuscular center from 2015 to 2019.

The study included 330 DM1 patients with a median age at 42.8 years (12.8). The mean pulmonary vital capacity (VC) was at 77.1% [22] of predicted value. The right and the left diaphragm ultrasound were significantly correlated [r 0.62, p < 0.001 for the diaphragm inspiratory motion (DIM)]. The VC was significantly associated with DIM (r 0.68, p < 0.0001) and sniff peak tissue Doppler diaphragm velocity (r = 0.43, p < 0.0001). A deep DIM < 57 mm can predict a VC<80% (AUC 0.83). A deep DIM <34 mm can predict a VC <50% (AUC 0.92). The DIM was significantly associated with gender (p = 0.001), BMI<25 kg/m² (p < 0.001), CTG repeat length (p < 0.001), Walton score ≥3 (p < 0.001), VC (p < 0.001), delta VC (p 0.05), PO2 (p < 0.001) and PCO2 (p < 0.001). In multivariate analysis, female gender (p < 0.001), Walton score ≥3 (p 0.006), CTG repeat length (p 0.026) and VC (p < 0.001) were significantly associated with DIM.

A single ultrasound focusing on diaphragm mechanics may select DM1 patients requiring complementary pulmonary function tests.